1. Field of the Invention
The invention relates to a discrete multi-tone (Dr system and, in particular, to an apparatus and a method for controlling initialization of the DMT system.
2. Background of the Related Art
The DMT scheme, the standard of an Asymmetric Digital Subscriber Loop (ADSL) communication environment, is a technique for performing a high-speed digital data communication at a transmission rate of 32 Kbps ˜8 Mbps via an ordinary telephone line. The DMT method has the characteristics of transmitting and receiving data at a frequency band (20 Kbps ˜1.104 Mbps) higher than a voice band, and transmitting data by allocating an optimum number of bits according to the Signal-to-Noise Ratio (SNR) of 256 sub-carriers (tones).
FIG. 1 is a schematic diagram illustrating a related DMT system. As illustrated in FIG. 1, the DMT system includes a central office (CO) 10 and remote terminal (RT) 20 connected to the central office 10 via a common communication line 17. The number of remote terminal 20 is variable. The CO 10 is connected to a personal computer (PC), and the CO 10 and the RT 20 include a DMT modem inside, respectively.
The DMT modem 100, as illustrated in FIG. 2, includes a transmitter 15 and a receiver 25. The transmitter 15 includes a transmitting frame processor 15-1 that processes data to be transmitted into signals by frame, a DMT modulator 15-2 that modulates the output of the transmitting frame processor 15-1 to a DMT form, a D/A converter 15-3 that converts the output of the DMT modulator 10-2 into analog signals, and a transmitting filter 154 that filters the output of the D/A converter 15-3 to thereby transmit it to the opposite party 30. In addition, the receiver 25 includes a receiving filter 25-1 that filters signals received from the opposite party 30, an A/D converter 25-2 that converts the output of the receiving filter into digital signals, a DMT demodulator 25-4 that demodulates the output of the A/D converter 25-2, and a receiving frame processor 25-4 that processes the output of the DMT demodulator 25-4 into signals by frame.
The operation of the conventional DMT system will be described as follows with reference to the accompanying drawings. In order for the CO 10 and the RT 20 to transmit and receive data from each other, an operation of initialization for setting a transmission speed and a transmission parameter with respect to the opposite party is performed. That is, as illustrated in FIG. 3 in step S10, either the CO 10 or the RT 20 performs an activation/acknowledgment procedure for recognizing whether or not it is connected with the opposite party. In step S11, when the opposite party is detected, either the CO 10 or the RT 20 performs a transceiver training procedure to tune an equalizer, an echo canceller and a timing recovery block of the local station.
When the above procedures are finished, in step S12 the CO 10 or the RT 20 measures the state of the common communication line 17 and performs a channel analysis process that computes a SNR condition of the common communication line 17 so as to compute the amount of information to be allocated to each transmission channel. In step S13, an exchange procedure is performed that exchanges the amount of transmission computed by the CO 10 and the RT 20 and communication parameters.
The above activation/acknowledgment procedure is performed by the DMT modulator 15-2 of FIG. 2. For example, the DMT modulator 15-2 of the RT 20 transmits a connection acknowledgment tone at a predetermined frequency to the CO 10 via the D/A converter 15-3 and the transmission filter 15. The CO 10 repeatedly detects the connection acknowledgment tone signal for a predetermined time period using a detector, and transmits a response tone signal of a predetermined frequency as an acknowledgment signal to the RT 20 if the connection acknowledgment tone signal transmitted from the RT 20 is detected. As a result, the RT 20 recognizes the connection with the CO 10 based on the reception of the response tone signal. If the RT 20 does not receive a response tone signal from the CO 10 for a certain time, the RT 20 repeatedly performs a procedure of detecting a response tone signal from the CO 10 after transmitting the same connection acknowledgment tone signal to the CO 10.
However, the conventional DMT system has a disadvantage in that a connection trial itself is in vain if the CO or the RT does not detect a response tone signal transmitted from the opposite party in the activation/acknowledgment procedure. Namely, there arises problems that too much noise is generated in the transmission band of a connection acknowledgment tone signal or a response tone signal, and, in the case of a line environment that occupies a particular frequency band and does not affect other frequency bands, communication by the DMT method is not possible.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.